Fossil and renewable energy fuels, such as oil, coal, gas and biomass, are burned or, in other words, combusted in order to produce energy. These combustible fuels may be utilized in internal combustion engines (such as spark ignited and compression ignition systems found in automobiles, trains, ships, planes, and generators), in turbine engines (used to power aircraft and ships), and in furnaces (such as burners, boilers, fluidized beds used in steam power plants).
The burning of combustible fuels to generate energy results in the generation of pollutants including CO, CO2, NOx (NO and NO2), particulate matter, sulfur compounds, and assorted hydrocarbons. These combustion pollutants are commonly exhausted to the atmosphere where they present a potential hazard to human health and the environment.
Monitoring of combustion processes and subsequent emissions within combustion chambers or their exhausts is extremely difficult because of the rapid build up of hydrocarbons and particulate matter on exposed surfaces within the combustion environment. It is vitally important to monitor these processes, however, in order to evaluate system parameters, optimize combustion performance, and provide feedback control, all of which are necessary to improve energy efficiency and limit pollutant emissions.
Many, if not all, of the emissions formed during combustion can be accurately and rapidly measured using standard optical methods (such as Fourier transform infrared spectroscopy and non-dispersive infrared analysis, for example). These technologies, however, require optical access to the exhaust stream of a combustion environment. Installation of a plain transparent optical access port or window into some component of the exhaust system would be futile because the build up of hydrocarbons and particulate matter would attach to and cloud the window on a frequent and regular basis. The accumulation of these contaminants on window surfaces is considered the primary barrier to the utilization of optical technologies in combustion and/or emission environments.
Most automotive emission sensors are solid-state devices that use a zirconia-based solid electrolyte to conduct oxygen atoms from one surface to the other. The response of these devices is dependent on the diffusion rate of oxygen atoms through the zirconia and this diffusion rate is limited due to the required thickness of the zirconia-based electrolyte. Because these sensors are diffusion limited, they have relatively slow time constants (>150 milliseconds) for producing data. In addition, since oxygen is the conducting medium, they are limited to the measurement of oxygen and some oxide gases (such as NOx), and therefore cannot be used to directly characterize hydrocarbons and particulate matter. These sensors also have poor resolution and are unable to measure concentrations below 10 parts-per-million.
It is highly desirable to measure hydrocarbons, particulate matter, and other gaseous emissions at time constants much less than 150 milliseconds. Optical-based sensors (such as those based on infrared spectroscopy) offer high speed (time constants <<150 milliseconds) and can be used to measure a range of pollutant species (including particulates) not detectable by currently available solid state devices. As noted earlier, many optical techniques are already well established and commercially available. The barrier to realizing optical diagnostic measurements lies with the constant fouling of the optical port, or window, due to the continual buildup of hydrocarbons and particulate matter.
During coal and oil combustion, visual monitoring takes place via portals in which clean air or an inert gas (such as nitrogen or argon) is constantly directed over the portal surface to maintain visibility. In spite of this, the portals nevertheless become contaminated over time and must be periodically cleaned. Another disadvantage of this technology is that a gas supply must be constantly directed over the portal. This necessitates a storage and supply system for the inert gas. A large percentage of the cost for these systems is associated with this gas usage.
Infrared detectors contain a detector that measures the intensity of infrared radiation. They are used to determine the presence of a flame during combustion (such as in gas/oil burners). Unfortunately, these detectors can also become contaminated with hydrocarbons and particulate matter and, as a result, must be frequently replaced. In fact, the accumulation of soot and/or hydrocarbons is considered a serious safety issue, since these detectors are considered unreliable when they become dirty.
As noted earlier, neither infrared detectors nor air guard portal systems are self-cleaning. Thus the combustion system must be stopped and/or at least partially dismantled in order for either an air guard portal system or an infrared detector to be cleaned or replaced on a regular basis.
In order to achieve maximum capability for any combustion/emission sensor system, one would need to install an optical access port, or window, containing an integrated self-cleaning system, into some component of the combustion/exhaust system. The self-cleaning capability of such a window would prevent and/or remove any buildup of hydrocarbons and particulate matter and thus maintain a clear optical access, or window, through which emissions may be measured.
U.S. Pat. No. 6,173,086 to Williams shows a vehicle window assembly that includes one or more resistance heating lines for electrically heating a section of the window area corresponding to a window wiper rest area. Williams' invention, however, would not work in the exhaust stream of a combustion environment because both hydrocarbons and particulate matter adhere too strongly to a surface to be wiped clean via mechanical action. Also, precision mechanical action would be limited if not impossible inside a combustion chamber, as the intense heat and pressure would interfere with mechanical movement and would likely severely damage any wiper assembly. Further, unlike the present invention which uses no mechanical action, Williams' invention centers around mechanical action. The present invention utilizes catalysis and thermophoretic action to prevent and/or remove hydrocarbon and particulate matter accumulation and maintain a clean surface.
U.S. Pat. No. 6,436,198 to Swain shows a method and apparatus for removing polymeric coatings from optical fiber by disposing the fiber within a low pressure environment and applying sufficient heat to volatilize at least a portion of the polymeric coating. This invention is, in essence, a vacuum furnace and therefore is unsuitable for use in a combustion environment, as one cannot achieve a vacuum during combustion. While Swain's invention does employ a heating grid, the present invention utilizes heat plus catalysis and Swain's invention uses heat plus vacuum.
U.S. Pat. No. 5,986,612 to Nagy shows a vehicle window antenna, comprised of a grid of conductive frit material affixed to the inner side of a window glass in a confined area above a window heating element comprising a grid of similar material similarly affixed and covering most of the window viewing area. While Nagy's invention utilizes a heating grid, the grid is not used to clean a surface, nor does Nagy's invention offer the application of catalysis in any way.
Accordingly, a need in the art exists for an integrated self-cleaning window assembly for monitoring gaseous and particulate matter emissions in a combustion environment while simultaneously preventing and removing the accumulation of carbon-based particulate matter and hydrocarbon condensation through a combination of catalysis and/or heat.